Genetic analysis of petal size through genomic manipulation in Brassica

The effect of genome composition and cytoplasm on petal size was studied in Brassica. Two accessions of Brassica rapa (2n = 20, AA) were reciprocally crossed with three accessions of Brassica oleracea (2n = 18, CC) to produce resynthesized B. napus (2n = 38, AACC or CCAA) and sesquidiploids (2n = 29, AAC or CAA). Petal size was measured and compared among diploids (AA and CC), sesquidiploids (AAC and CAA) and amphidiploids(AACC and CCAA). The results showed that petal size is a genome-dependent and highly heritable character. The heritability of petal length is as high as 96.3%. The addition of each C-genome to the AA genomic background increased the petal length by 4-5 mm. Cytoplasm of B. oleracea showed a positive effect on petal length by about 1.3 mm over that of B. rapa. Petal width was positively correlated with petal length at a highly significant level (r = 0.806, df = 81). Resynthesized B. napes (AACC) showed significantly larger flower petals than natural rapeseed cultivars (AACC).